Vertical beam emitting marker for a sports field

ABSTRACT

A marker for a sports field comprising an elongated substantially vertical device for marking a field position associated with a game playable on the sports field using an object that may become airborne. The field position is used to determine compliance of the object when airborne with a rule of the game. The apparatus also comprises a source for emitting an elongated generally vertical beam of electromagnetic radiation adjacent to the device to help mark the field position.

RELATED APPLICATION

This application claims priority from U.S. Provisional Application No. 61/108,973, filed Oct. 28, 2008.

FIELD OF THE INVENTION

The present invention relates to a marker for a sports field and a method for marking a sports field and, more particularly, to a sports field marker that emits a substantially vertical beam of electromagnetic radiation and a method for marking a sports field by emitting a substantially vertical beam of electromagnetic radiation.

BACKGROUND OF THE INVENTION

Various games played on sports fields use objects, such as balls, that may be become airborne. The rules of such games may involve determining whether such balls or other game objects, when airborne, cross one or more positions on the sports field. The positions are typically marked with visible devices, which may be structures, such as goal posts, or non-structural indicia, such as paint. The visibility of such position markers may be limited during the course of a game due to environmental factors, such as wind, rain, snow, and darkness, or due to heavy foot traffic by participants in the game. The limited visibility of the position markers may affect proper officiating of the game by referees and other game officials.

To assist game officials by supplementing field position markers that are applied to the surface of a sports field, it has been proposed, for example, in U.S. Pat. No. 3,741,662, to provide horizontally directed beams of visible light generated by lasers. It also been proposed, for example, in U.S. Pat. No. 6,895,677, to provide a visible line on the surface of a sports field using lasers positioned above the field, directed downward at the field, and moved so as to cause the beams of light from the lasers to traverse the field. To assist with officiating in connection with determining goals in a game, it has been proposed, for example, in U.S. Pat. No. 7,115,053, to provide wide angle beams of visible light that illuminate either an area outside of and around a goal scoring area or the goal scoring area itself.

SUMMARY OF THE INVENTION

The present invention is directed to a marker for a sports field and a method for marking a sports field and, more particularly, to a sports field marker that emits a substantially vertical beam of electromagnetic radiation and a method for marking a sports field by emitting a substantially vertical beam of electromagnetic radiation.

In accordance with an embodiment of the present invention, a marker for a sports field comprises an elongated substantially vertical device for marking a field position associated with a game playable on the sports field using an object that may become airborne. The field position is used to determine compliance of the object when airborne with a rule of the game. The apparatus also comprises a source for emitting an elongated generally vertical beam of electromagnetic radiation adjacent to the device to help mark the field position.

In accordance with another embodiment of the present invention, a marker for a sports field comprises a device with an elongated substantially vertical portion for marking a field position associated with a game playable on the sports field using an object that may become airborne. The field position is used to determine compliance of the object when airborne with a rule of the game. The device includes a member with an exterior surface that is elongated in one direction and that is defined by a closed curve in a plane substantially perpendicular to the one direction. The marker also comprises a source for emitting a generally vertical beam of electromagnetic radiation adjacent to the device and an electromagnetic radiation detector for detecting electromagnetic radiation generated by the source and reflected by the object when passing through the beam of electromagnetic radiation. The source and the electromagnetic radiation detector are disposed within the exterior surface of the member.

In accordance with still another embodiment of the invention, a method is provided for marking a field position on a sports field associated with a game playable on the sports field using an object that may become airborne. The field position is used to determine compliance of the object when airborne with a rule of the game. The method comprises the steps of positioning an elongated substantially vertical device to mark the field position and emitting an elongated generally vertical beam of electromagnetic radiation adjacent to the device to help mark the field position.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the present invention will become apparent to one skilled in the art upon consideration of the following description of the invention and the accompanying drawings, in which:

FIG. 1 is a frontal view of a first embodiment of a marker in accordance with the present invention;

FIG. 2 is a side view of the marker of FIG. 1;

FIG. 3 is an enlarged schematic view of a portion of the marker of FIG. 1;

FIG. 4 is an enlarged schematic view of a portion of a second embodiment of a marker in accordance with the present invention;

FIG. 5 is an enlarged schematic view of a portion of a third embodiment of a marker in accordance with the present invention;

FIG. 6 is a frontal view of a fourth embodiment of a marker in accordance with the present invention;

FIG. 7 is a side view of the marker of FIG. 6;

FIG. 8 is a frontal view of a fifth embodiment of a marker in accordance with the present invention;

FIG. 9 is a frontal view of a sixth embodiment of a marker in accordance with the present invention;

FIG. 10 is a frontal view of a seventh embodiment of a marker in accordance with the present invention; and

FIG. 11 is an enlarged schematic view of a portion of an eighth embodiment of a marker in accordance with the present invention.

DETAILED DESCRIPTION

FIGS. 1 through 3 illustrate a marker 10 for a sports field 12, in accordance with an example of the present invention. The marker 10 includes a device 14 for marking a field position associated with a game playable on the sports field 12 with an object that may become airborne. More particularly, the device 14 is part of a goal post 16 for the game of American football. The goal post 16 includes two substantially vertical uprights 18 and 20, a cross bar 22 connecting lower ends of the uprights, and a gooseneck 24 supporting the uprights and the cross bar. One end of the gooseneck 24 is connected at or about the midpoint of the cross bar 22. The gooseneck 24 extends downward and rearward from the cross bar 22 to an end that is mounted on the sports field 12.

The uprights 18 and 20 and cross bar 22 are used to determine whether a football (not shown), when kicked, has complied with the football rule concerned with, for example, scoring a field goal. The relevant rule generally requires the football to pass through a space defined by the uprights 18 and 20 and the cross bar 22. More particularly, the rule requires the football to pass above the cross bar 22 and between the uprights 18 and 20. A properly kicked football will be considered to pass between the uprights 18 and 20 even if the football passes above the cross bar 22 at a height greater than the height of the uprights. Evaluation of whether a football has passed between the uprights 18 and 20 of the goal post 16 when kicked to a height greater than the height of the uprights requires judgment on the part of the game official charged with determining whether the field goal attempt has been successful. This judgment can be particularly difficult when environmental conditions are less than optimal, e.g., after sunset, during rain or snow, or during high winds.

The marker 10 of the present invention helps game officials judge whether, for example, a kicked football, when airborne, has complied with the game rule associated with scoring a field goal. Each of the two uprights 18 and 20 of the goal post 16 is a substantially vertical device 14 for marking a field position associated with scoring a field goal in football. The vertical dot-dash lines 26 in FIG. 1 represent vertical extensions of the uprights 18 and 20 beyond their respective ends between which a football would have to pass to comply with the rule concerning scoring a field goal. The marker 10 of the present invention helps to make vertical extensions of the uprights 18 and 20 visible, either to the human eye or to a sensor or to both.

In accordance with the embodiment of the invention shown in FIGS. 1-3, the marker 10 includes one or more emitter-detector modules 28. At least one emitter-detector module 28 may be associated with each substantially vertical device 14 or upright 18, 20 for marking a field position that will be used to determine whether a field goal has been scored. As shown in FIG. 1, four emitter-detector modules 28 are mounted on the goal post 16. One emitter-detector module 28 is mounted in a position 30 at or near the upper end of the left upright 18 (as viewed in FIG. 1). A second emitter-detector module 28 is mounted in a position 32 at or near the upper end of the right upright 20 (as viewed in FIG. 1). A third emitter-detector module 28 is mounted in a position 34 adjacent the intersection of the lower end of the left upright 18 and the cross bar 22. A fourth emitter-detector module 28 is mounted in a position 36 adjacent the intersection of the lower end of the right upright 20 and the cross bar 22.

As shown in FIG. 3, each emitter-detector module 28 includes a source 38 for emitting electromagnetic radiation, such as light, and a detector 40 for detecting electromagnetic radiation, such as light. Each emitter-detector module 28 also includes a cover 42 that is transparent to the electromagnetic radiation emitted by the source 38 and detected by the detector 40. The cover 42 is connected by a shaft 44 to an electric motor 46. The cover 42 closes an open end of a cylindrical housing 48 that encloses the source 38, the detector 40, the shaft 44, and the electric motor 46. A power supply and communication sub-module 50 is mounted at the end of the housing 48 opposite the cover 42. The emitter-detector module 28 may also include a shutter (not shown) mounted above the cover 42 to block at least certain types of electromagnetic radiation from the detector 40 when it is not in use.

Each emitter-detector module 28 may be shaped and dimensioned to permit mounting to the goal post 16 in a relatively unobtrusive manner. For example, the emitter-detector modules 28 at positions 30 and 32 may have outer dimensions, such as diameter and circumference, that are substantially the same as the outer dimensions of the uprights 18 and 20 so that the emitter-detector modules may be mounted at the ends of the uprights. Alternatively, because many goal posts are formed from tubular materials, such as aluminum tubing, the emitter-detector modules 28 may be shaped and dimensioned to fit within the tubular structure of the uprights 18 and 20 and/or cross bar 22. For example, the emitter-detector modules 28 at positions 30 and 32 may have outer dimensions, such as diameter and circumference, that are slightly smaller than the inner dimensions of the tubular walls of the uprights 18 and 20 so that the emitter-detector modules may be fitted within the ends of the uprights with the covers 42 uppermost. Each of the uprights 18 and 20 is, in effect, a pole with a substantially vertical central axis and an exterior surface that is at least partially defined by a closed curve in a plane substantially perpendicular to said central axis. The emitter-detector modules 28 at positions 30 and 32 are thus disposed within a space defined by the closed curve extended in opposed directions along the central axis.

With either of the foregoing mounting arrangements, the cover 42 of each of the emitter-detector modules 28 at positions 30 and 32 may be directly exposed to the ambient atmosphere. To assist in deflecting or removing rain, snow, dust and other materials from the cover 42, the cover may be rotated at an appropriate speed by the electric motor 46 via the shaft 44. In addition, a closable shutter (not shown) may be used to shield the cover 42 and the rest of the emitter-detector module 28 from ambient weather conditions, dust, dirt and other materials when the emitter-detector module is not in use.

If the cross bar 22 of the goal post 16 is formed of tubular material, the emitter-detector modules 28 at positions 34 and 36 may be mounted inside the cross bar, either in an upright orientation, as shown in FIG. 1, or in a horizontal orientation. A horizontal orientation may require an additional mirror, lens or waveguide (not shown) to redirect the light or other electromagnetic radiation from the source 38. Regardless of the orientation of the emitter-detector modules 28 at positions 34 and 36, however, an opening, such as a slit, (not shown) may be formed in the cross bar 22 at each position 34 and 36 to permit light or other electromagnetic radiation to exit and enter the emitter-detector modules. Alternatively, the emitter-detector modules 28 at positions 34 and 36 may be aligned to permit light or other electromagnetic radiation to exit and/or enter the emitter-detector modules by traveling lengthwise through the uprights 18 and 20.

The source 38 of electromagnetic radiation in each emitter-detector module 28 may emit a beam of broad-spectrum light, including both visible and infrared light. The detector 40 may include a CCD camera, which may receive or detect all of the light wave lengths emitted by the source 38 or which may receive or detect only certain light wave lengths, such as, for example, infrared wave lengths or wave lengths associated with a narrow color band. Selection of the light wave lengths received by the detector 40 may be achieved by mounting an appropriate filtering lens (not shown) on the CCD camera. The beam of light emitted by the source 38 is a relatively narrow beam that may have a diameter and circumference at the source no greater than the diameter and circumference of the uprights 18 and 20. The beam may be focused so that the diameter of the beam does not substantially increase over distances up to fifty meters.

In FIG. 1, a representative substantially vertical beam 52 of light is shown being emitted from the emitter-detector module 28 at position 30, and a second representative substantially vertical beam 54 of light is shown being emitted from the emitter-detector module 28 at position 34. As is apparent from FIG. 1, the beams 52 and 54 are upwardly directed and are substantially parallel to the substantially vertical upright 18. Although the beam 54 is shown as being wider at its upper end than the beam 52, this is for clarity of illustration only and may not be representative of the actual beam diameters. As is also apparent from FIG. 1, a beam of visible light such as beam 52 will provide a visible extension of the upright 18 for the assistance of game officials. As will be explained, the beam 52 may also provide input for the detector 40 to determine the position of the football (not shown) relative to the upright 18 and its light beam extension.

The source 38 in each emitter-detector module 28 is disposed adjacent one side of the housing 48 and emits light in a substantially vertical direction. The cover 42 is disposed above the source 38 and is transparent to the light emitted by the source. In order to have an edge of the beam of light emitted by the source 38 aligned with the edge of the upright 18 or 20, a portion of the cover 42 immediately above the source may be formed as a Fresnel lens. The Fresnel lens portion of the cover 42 is configured to redirect the light from the source 38 so that an edge of the light beam is aligned with an edge of the upright 18 or 20, as indicated by the dashed line in FIG. 3. The detector 40 is aligned at a small, predetermined angle to and distance from the substantially vertical beam of light from the source 38. If the beam of light is interrupted by an object, such as a football, passing through beam, light from the beam may be reflected by the object back toward the detector 40. The detector 40 receives the reflected light and transmits an electronic signal indicative of the intensity, angle of incidence and other characteristics of the reflected light to a microprocessor or computer 56.

The microprocessor or computer 56 may be entirely separate and spaced away from the emitter-detector module 28, as shown in FIG. 3. In such a construction, the microprocessor or computer 56 may communicate with the emitter-detector module 28 via one or more communication cables 58 or, as an alternative, via wireless communication. As another alternative, the microprocessor or computer 56 may be incorporated in the power supply and communication sub-module 50 of the emitter-detector module 28 to perform some or all of the functions performed by a remotely-located microprocessor or computer. The extent to which the microprocessor or computer 56 or its functions can be incorporated in the emitter-detector module 28 is determined by the nature and extent of the computations required. The more computations required, the more likely it is that the computations will have to be performed by a remote computer 56, rather than a microprocessor located in the power supply and communication sub-module 50.

The microprocessor or computer 56 uses the information in the signal from the detector 40 to make a determination whether the reflected light received by the detector 40 is reflected from a football or some other object, such as a bird. The microprocessor or computer 56 may also use the information in the signal from the detector 40 to determine the position of the object, such as a football, from which the light received by the detector was reflected. Based on the angle at which the reflected light was received and on the known, predetermined angle and distance between the beam of light from the source 38 and the detector 40, the position of the object can be determined via triangulation. If the microprocessor or computer 56 determines that the reflected light received by the detector 40 was reflected by a football, the microprocessor or computer may determine that some portion of the football entered the beam of light from the source 38. From such a determination, the microprocessor or computer 56 may, in turn, determine that the football did not stay between the uprights 18 and 20 and therefore the attempted field goal was not successful. Alternatively or additionally, the microprocessor or computer 56 may determine the position of the football, via triangulation, for example, and compare the determined position of the football to the position of the uprights 18 and 20 stored in memory. From the foregoing comparison, the microprocessor or computer 56 may determine whether or not the attempted field goal was successful. All of the information provided to the microprocessor or computer 56 and all of the determinations made by the microprocessor or computer may be stored in a memory device (not shown) for concurrent or later retrieval and reference via, for example, a visual display device (not shown). Such a memory device may be included in or separate from the microprocessor or computer. The visual display device may be, for example, a cathode ray tube display, a liquid crystal display, or a light emitting diode display.

As will be apparent from the foregoing, the embodiment of the marker 10 shown in FIGS. 1-3 permits several potential levels of assistance to game officials and/or several different levels of redundancy. For example, the emitter-detector modules 28 located at positions 30 and 32 may emit beams of visible light, such as beam 52, to extend the uprights 18 and 20 and give game officials visible markers for judging, for example, a field goal attempt. Alternatively or additionally, the emitter-detector modules 28 at positions 30 and 32 may emit beams of visible and/or non-visible (e.g., infrared) light and may use light reflected from such beams to judge whether a football has entered or crossed either of the beams and therefore not passed between the uprights 18 and 20. The emitter-detector modules 28 at positions 34 and 36 may be used to make determinations to supplement the determinations made by the emitter-detector modules 28 at positions 30 and 32, respectively, or to provide redundancy in the event one or both of the modules at positions 30 and 32 experiences a malfunction. The emitter-detector modules 28 at positions 34 and 36 may also emit and detect only non-visible light of wavelengths not emitted or detected by the emitter-detector modules 28 at positions 30 and 32. Still further, the marker 10 may use only the emitter-detector modules 28 at positions 30 and 32 or only the emitter-detector modules 28 at positions 34 and 36, rather than using emitter-detector modules at all four positions.

To further assist game officials and operators or technicians responsible for proper operation of the marker 10 and to provide information to spectators at a football game, the marker may include one or more indicator lamps 37 at the lower ends of the uprights 18 and 20 below the cross bar 22. The indicator lamps 37 may provide status indications by, for example, emitting light of different colors associated with different events or the status of the marker 10. For example, the indicator lamps 37 may emit a visible yellow light to indicate that the marker is functioning properly and ready for use, a visible green light to indicate that the marker has detected a successful field goal attempt, and a visible red light to indicate that the marker has detected an unsuccessful field goal attempt. The indicator lamps 37 may also emit a flashing red light to indicate that the marker 10 is experiencing a malfunction or is not yet ready for use. Each indicator lamp 37 may emit light of different colors and may be capable of operating in both flashing and non-flashing modes. Alternatively, each indicator lamp 37 may emit light of a specific color, and more than one lamp may be provided so as to display the various colored-coded indications described above.

FIG. 4 illustrates an emitter-detector module 128 that is constructed in accordance with a second example of the present invention. As can be seen in FIG. 4, the emitter-detector module 128 is outwardly similar in construction to the emitter-detector module 28 of FIG. 3. In particular, the emitter-detector module 128 includes a cylindrical housing 148 with an upper open end that is closed by a cover 142. A power supply and communication sub-module 150 is mounted at the end of the housing 148 opposite the cover 142. Inside the housing 148, however, the emitter-detector module 128 includes a laser sensor unit 160 that both acts as a source for emitting electromagnetic radiation, specifically a beam of laser light, and a detector for detecting such electromagnetic radiation. Such a laser sensor unit 160 is commercially available as a “time of flight” sensor. To orient the laser beam from the laser sensor unit 160 in the proper direction, the emitter-detector module 128 includes one or more mirrors 162, two of which are shown in FIG. 4. The mirrors 162 may be adjustable, either manually or via an electrically or pneumatically powered motor (not shown), to change the orientation of the beam. The cover 142 is transparent to the laser light emitted by the laser sensor unit 160. The emitter-detector module 128 may also include a shutter (not shown) mounted above the cover 142 to block at least certain types of electromagnetic radiation from the laser sensor unit 160 when it is not in use.

Proper orientation of the mirrors 162 permits a beam of laser light 164 emitted by the laser sensor unit 160 to be aligned so that an edge of the light beam is aligned with an edge of the upright 18 or 20, as indicated by the dashed line in FIG. 4. If the beam of light 164 is interrupted by an object, such as a football, passing through the beam, light 166 from the beam may be reflected by the object back toward the mirrors 162 and, therefore, toward the laser sensor unit 160, as indicated by the dotted line in FIG. 4. The laser sensor unit 160 receives the reflected light 166 and transmits an electronic signal indicative of the intensity, angle of incidence and other characteristics of the reflected light to a microprocessor or computer 156 via one or more communication cables 158 or, alternatively, via wireless communication. The microprocessor or computer 156 uses the information in the signal from the laser sensor unit 160 to make a determination whether the reflected light received by the laser sensor unit 160 is reflected from a football or some other object, such as a bird. The microprocessor or computer 156 may also use the information in the signal from the laser sensor unit 160 to determine, via triangulation, the position of the object, such as a football, from which the light received by the laser sensor unit was reflected.

If the microprocessor or computer 156 determines that the reflected light received by the laser sensor unit 160 was reflected by a football, the microprocessor or computer may determine that some portion of the football entered the beam of laser light 164. From such a determination, the microprocessor or computer 156 may, in turn, determine that the football did not stay between the uprights 18 and 20 and therefore the attempted field goal was not successful. Alternatively or additionally, the microprocessor or computer 156 may determine the position of the football, via triangulation, for example, and compare the determined position of the football to the position of the uprights 18 and 20 stored in memory. From the foregoing comparison, the microprocessor or computer 156 may determine whether or not the attempted field goal was successful. All of the information provided to the microprocessor or computer 156 and all of the determinations made by the microprocessor or computer may be stored in a memory device, which may be included in or separate from the microprocessor or computer, for concurrent or later retrieval and reference via, for example, a visual display device.

FIG. 5 illustrates an emitter-detector module 228 that is constructed in accordance with a third example of the present invention. As can been seen in FIG. 5, the emitter-detector module 228 is similar in construction to the emitter-detector module 128 of FIG. 4. In particular, the emitter-detector module 228 includes a cylindrical housing 248 with an upper open end that is closed by a cover 242. A power supply and communication sub-module 250 is mounted at the end of the housing 248 opposite the cover 242. The emitter-detector module 228 also includes a laser sensor unit 260 that both acts as a source for emitting electromagnetic radiation, specifically a beam of laser light, and a detector for detecting such electromagnetic radiation. To orient the laser beam from the laser sensor unit 260 in the proper direction, the emitter-detector module 228 includes one or more mirrors 262, one of which is shown in FIG. 5 and which may be adjustable, either manually or via an electrically or pneumatically powered motor (not shown), to change the orientation of the beam. The cover 242 is transparent to the laser light emitted by the laser sensor unit 260. The emitter-detector module 228 may also include a shutter (not shown) mounted above the cover 242 to block at least certain types of electromagnetic radiation from the laser sensor unit 260 when it is not in use.

Unlike the emitter-detector module 128 of FIG. 4, the emitter-detector module 228 of FIG. 5 includes, within the housing 248, a rotatable mirror 270, an electric motor 272, and a shaft 274 connecting the electric motor to the mirror. Rotation of the mirror 270 by the electric motor 272 effectively causes the laser light emitted by the laser sensor unit 260 to pulse. The pulses of the beam of laser light 264 emitted by the laser sensor unit are indicated by the multiple dashed lines in FIG. 5. Although the dashed lines are shown as being spread apart, this is for illustration purposes only. The beam of laser light 264 may not have any greater diameter than the beam of light 164 emitted by the laser sensor unit 160 of FIG. 4.

Proper orientation of the mirror 262 permits a beam of laser light 264 emitted by the laser sensor unit 260 to be aligned so that an edge of the light beam is aligned with an edge of the upright 18 or 20, as indicated by the leftmost dashed line in FIG. 5. If the beam of laser light 264 is interrupted by an object, such as a football, passing through the beam, light from the beam may be reflected by the object back toward the mirror 262 and, therefore, toward the laser sensor unit 260. The laser sensor unit 260 receives the reflected light and transmits an electronic signal indicative of the intensity, angle of incidence and other characteristics of the reflected light to a microprocessor or computer 256 via one or more communication cables 258 or, alternatively, via wireless communication. The microprocessor or computer 256 uses the information in the signal from the laser sensor unit 260 to make a determination whether the reflected light received by the laser sensor unit 260 is reflected from a football or some other object, such as a bird. The microprocessor or computer 256 may also use the information in the signal from the laser sensor unit 260 to determine, via triangulation, the position of the object, such as a football, from which the light received by the detector was reflected.

If the microprocessor or computer 256 determines that the reflected light received by the laser sensor unit 260 was reflected by a football, the microprocessor or computer may determine that some portion of the football entered the beam of laser light 264. From such a determination, the microprocessor or computer 256 may, in turn, determine that the football did not stay between the uprights 18 and 20 and therefore the attempted field goal was not successful. Alternatively or additionally, the microprocessor or computer 256 may determine the position of the football, via triangulation, for example, and compare the determined position of the football to the position of the uprights 18 and 20 stored in memory. From the foregoing comparison, the microprocessor or computer 256 may determine whether or not the attempted field goal was successful. All of the information provided to the microprocessor or computer 256 and all of the determinations made by the microprocessor or computer may be stored in a memory device, which may be included in or separate from the microprocessor or computer, for concurrent or later retrieval and reference via, for example, a visual display device.

FIGS. 6 and 7 illustrate a marker 110 that is constructed in accordance with a fourth example of the present invention. As shown in FIGS. 6 and 7, the marker 110 includes two emitter-detector modules 28 that are mounted below the uprights 18 and 20 and cross bar 22 of a goal post 16 and at or near the surface of the sports field 12. One emitter-detector module 28 is mounted in a position 180 below and slightly behind the left upright 18. A second emitter-detector module 28 is mounted in a position 182 below and slightly behind the right upright 20 (as best shown in FIG. 7). Each emitter-detector module 28 emits an upwardly directed and substantially vertical beam 184 of light or other electromagnetic radiation that is substantially parallel to an associated upright 18 or 20.

The positions 180 and 182 may be selected so that the beams 184 may be as close as possible to the uprights 18 and 20 while not being partially blocked by the uprights. As the positions 180 and 182 are not positions on the uprights 18 and 20, the beams 184 of light from the emitter-detector modules 28 are not affected by movement of the uprights, such as may be caused by wind. Therefore, if desired, the beams 184 of light may be used to determine whether, for example, an attempted field goal has been successful without having to consider temporary movements of the uprights 18 and 20 caused by wind, for example, which may occur between the time that a football is kicked and the time at which the football reaches the goal post 16. Alternatively, the uprights 18 and 20 may be hollow throughout their respective lengths and have open upper and lower ends. With such a construction of the uprights 18 and 20, the positions 180 and 182 may be selected so that the beams 184 extend substantially vertically through the uprights and project out of the open upper ends of the uprights. To help maintain such an alignment of the beams 184 and open ends of the uprights 18 and 20, the goal post 16 may be used on a sports field in a covered or partially covered stadium or a stadium otherwise protected from high winds that might cause the uprights to move relative to the beams.

Although the marker 110 shown in FIGS. 6 and 7 is illustrated as including emitter-detector modules 28 of the type shown in FIG. 3, the marker 110 may alternatively or additionally include emitter-detector modules 128 and/or 228 of the types shown in FIGS. 4 and 5, respectively. Additionally, the marker 110 may include emitter-detector modules 28, 128 and/or 228 at positions corresponding to positions 30 and 32 and/or positions 34 and 36 of FIG. 1 to provide several potential levels of assistance to game officials and/or several different levels of redundancy. For example, emitter-detector modules 28 located at positions corresponding to positions 30 and 32 of FIG. 1 may emit beams of visible light to extend the uprights 18 and 20 and give game officials visible markers for judging, for example, a field goal attempt, while the emitter-detector modules 28 at positions 180 and 182 may emit beams of non-visible (e.g., infrared) light and may use light reflected from such beams to judge whether a football has entered or crossed either of the beams and therefore not passed between the uprights 18 and 20. Emitter-detector modules 28 at positions corresponding to positions 30 and 32 and/or 34 and 36 of FIG. 1 may be used to make determinations to supplement the determinations made by the emitter-detector modules 28 at positions 180 and 182, respectively, or to provide redundancy in the event one or both of the modules at positions 180 and 182 experiences a malfunction. Emitter-detector modules 28 at positions corresponding to positions 30 and 32 and/or positions 34 and 36 of FIG. 1 may also emit and detect only non-visible light of wavelengths not emitted or detected by the emitter-detector modules 28 at positions 180 and 182.

As yet a further alternative, the marker 110 may include reflectors 186 mounted above and in alignment with the beams 184 from the emitter-detector modules 28 at positions 180 and 182 or in alignment with emitter-detector modules (not shown) at positions corresponding to positions 30 and 32 and/or 34 and 36 of FIG. 1. The reflectors 186 reflect light emitted from the emitter-detector modules 28 back to the emitter-reflector modules. Use of reflectors 186 permits a greater effective height for the beams 184 and also permits detection of the presence of a football or other object in the beams by virtue of a football or other object fully or partially blocking the light that is reflected from the reflectors 186.

FIG. 8 illustrates a marker 210 that is constructed in accordance with a fifth example of the present invention. As shown in FIG. 8, the marker 210 includes a vertically oriented emitter-detector module 28 mounted in the position 30 at or near the upper end of the left upright 18 (as viewed in FIG. 8). A second vertically oriented emitter-detector module 28 is mounted in the position 32 at or near the upper end of the right upright 20 (as viewed in FIG. 8). A third emitter-detector module 28 is mounted in the position 34 in a generally horizontal orientation adjacent the intersection of the lower end of the left upright 18 and the cross bar 22. A fourth emitter-detector module 28 is mounted in the position 36 in a generally horizontal orientation adjacent the intersection of the lower end of the right upright 20 and the cross bar 22.

As with the marker 10 illustrated in FIG. 1, a representative substantially vertical beam 252 of light or other electromagnetic radiation is shown being emitted from the emitter-detector module 28 at position 30, and a second representative substantially vertical beam 254 of light or other electromagnetic radiation is shown being emitted from the emitter-detector module 28 at position 34. As is apparent from FIG. 8, the beams 252 and 254 are upwardly directed and are substantially parallel to the substantially vertical upright 18. Unlike the marker 10 of FIG. 1, however, the beam 254 is both shown as being wider at its upper end than the beam 252 and is, in fact, wider.

The beam 252 includes visible light and may include light of wave lengths not visible to the human eye. The beam 254 includes only light of wave lengths not visible to the human eye, such as infrared light. The beam 252 of visible light may provide a visible extension of the upright 18 for the assistance of game officials. The beam 254 of non-visible light provides light that may be reflected by an object, such as a football, passing through the beam back toward the detector (not shown) of the emitter-detector module 28. An electronic signal from the detector (not shown) which is indicative of the intensity, angle of incidence and other characteristics of the reflected light, may be provided to a microprocessor or computer (not shown).

The microprocessor or computer (not shown), in turn, may determine the position of the football, via triangulation, for example, and compare the determined position of the football to the position of the uprights 18 and 20 stored in memory. From the foregoing comparison, the microprocessor or computer may determine whether or not the attempted field goal was successful. The greater width of the beam 254 of non-visible light, as compared to the beam 252 of visible light, permits the emitter-detector modules 28 mounted at positions 34 and 36 to detect an object, such as a football, in a larger field of view and provide more data to the microprocessor or computer (not shown). All of the information provided to the microprocessor or computer and all of the determinations made by the microprocessor or computer may be stored in a memory device, which may be included in or separate from the microprocessor or computer, for concurrent or later retrieval and reference via, for example, a visual display device.

FIG. 9 illustrates a marker 310 that is constructed in accordance with a sixth example of the present invention. As shown in FIG. 9, the marker 310 includes an emitter-detector module 28 is mounted in the position 30 at or near the upper end of the left upright 18 (as viewed in FIG. 9). A second emitter-detector module 28 is mounted in the position 32 at or near the upper end of the right upright 20 (as viewed in FIG. 9). A third emitter-detector module 28 is mounted in a position 390 adjacent the intersection of the upper end of the gooseneck 24 and the cross bar 22.

As with the marker 10 illustrated in FIG. 1, a representative substantially vertical elongated beam 352 of light or other electromagnetic radiation is shown being emitted from the emitter-detector module 28 at position 30. The beam 352 is upwardly directed and is substantially parallel to the upright 18. A second upwardly-directed, generally vertical representative beam 392 of light or other electromagnetic radiation is shown being emitted from the emitter detector module 28 at position 390 located between the uprights 18 and 20. The beam 392 is both shown as being wider at its upper end than the beam 352 and is, in fact, substantially wider than the beam 352. The generally vertical, relatively wide, fan-shaped beam 392 of light thus provides light adjacent to the upper end of each of the uprights 18 and 20. Because the fan-shaped beam 392 of light is intended to illuminate the area adjacent to and above the upper ends of the uprights 18 and 20, the beam 392 need not and does not illuminate all of the area between the uprights 18 and 20 and above the cross bar 22.

The beam 352 includes visible light and may include light of wave lengths not visible to the human eye. The beam 392 may include only light of wave lengths not visible to the human eye, such as infrared light. The substantially vertical elongated beam 352 of visible light may provide a visible extension of the upright 18 for the assistance of game officials. The generally vertical, relatively wide, fan-shaped beam 392 of non-visible light provides light adjacent to the upper end of each of the uprights 18 and 20.

The non-visible light of the beam 392 may be reflected by an object, such as a football, passing through the beam back toward the detector (not shown) of the emitter-detector module 28. An electronic signal from the detector (not shown) which is indicative of the intensity, angle of incidence and other characteristics of the reflected light, to a microprocessor or computer (not shown).

The microprocessor or computer (not shown), in turn, may determine the position of the football, via triangulation, for example, and compare the determined position of the football to the position of the uprights 18 and 20 stored in memory. From the foregoing comparison, the microprocessor or computer may determine whether or not the attempted field goal was successful. The much greater width of the beam 392 of non-visible light, as compared to the elongated beam 352 of visible light, permits the emitter-detector module 28 mounted at position 190 to detect an object, such as a football, in a larger field of view, which includes the upper ends of both uprights 18 and 20, and provide more data to the microprocessor or computer (not shown). All of the information provided to the microprocessor or computer and all of the determinations made by the microprocessor or computer may be stored in a memory device, which may be included in or separate from the microprocessor or computer, for later retrieval and reference via, for example, a visual display device.

FIG. 10 illustrates a marker 410 that is constructed in accordance with a seventh example of the present invention. As shown in FIG. 10, the marker 410 includes a device 414 for marking a field position associated with a game playable on the sports field 12 with an object that may become airborne. More particularly, the device 414 is part of a foul pole 416 for the game of baseball. The foul pole 416, as shown, includes a single substantially vertical upright 418, which may be formed of a tubular material, such as aluminum tubing. The device 414 and the foul pole 416 may alternatively simply be a line painted or otherwise marked on another structure, such a portion of a baseball stadium. The upright 418 is used to determine whether a baseball (not shown), when batted, has complied with the baseball rule concerned with whether the baseball has stayed within fair territory and within the baseball playing field. The relevant rule requires the baseball to remain on one side of the foul pole 416. Evaluation of whether a baseball has remained on the fair side of the foul pole 416 when batted to a height greater than the height of the foul pole requires judgment on the part of the game official charged with determining whether the baseball has stayed within the playing field. This judgment can be particularly difficult when environmental conditions are less than optimal, e.g., after sunset or during rain.

An emitter-detector module 28 may be mounted in a position 430 at or near the upper end of the upright 418. A second emitter-detector module 28 may be mounted in a position 434 partway along the length of the upright 418. A third emitter-detector module 28 may be mounted in a position 480 at the lower end of the upright 418 and at or near the surface of the sports field 12. Although the marker 410 is illustrated as including emitter-detector modules 28 of the type shown in FIG. 3, the marker 410 may alternatively or additionally include emitter-detector modules 128 and/or 228 of the types shown in FIGS. 4 and 5, respectively. At least the emitter-detector module 28 at the position 430 may have outer dimensions, such as diameter and circumference, that are substantially the same as the outer dimensions of the upright 418 so that the emitter-detector module may be mounted at the end of the upright. Alternatively, the emitter-detector module 28 may be shaped and dimensioned to fit within the tubular structure of the upright 418. For example, the emitter-detector module 28 may have outer dimensions, such as diameter and circumference, that are slightly smaller than the inner dimensions of the tubular walls of the upright 418 so that the emitter-detector module may be fitted within the end of the upright.

Only one or only two of the three emitter-detector modules 28 shown in FIG. 10 may be used or all three of the emitter-detector modules may be used to provide several potential levels of assistance to game officials and/or several different levels of redundancy. For example, the emitter-detector module 28 located at position 430 may emit an upwardly directed and substantially vertical beam of visible light to extend the upright 418 and give game officials a visible marker for judging, for example, a foul ball. At the same time, emitter-detector modules 28 at positions 434 and 480 may emit upwardly directed and substantially vertical beams of non-visible (e.g., infrared) light substantially parallel to the upright 418 and may use light reflected from such beams to judge whether a baseball has entered or crossed either of the beams and therefore passed beyond the upright 418 into foul territory. Emitter-detector modules 28 at positions 434 and/or 480 may be used to make determinations to supplement the determination made by the emitter-detector module 28 at position 430 or to provide redundancy in the event the module at position 430 experiences a malfunction. Emitter-detector modules 28 at positions 434 and/or 480 may also emit and detect only non-visible light of wavelengths not emitted or detected by the emitter-detector module 28 at position 430.

As yet a further alternative, the marker 410 may include a reflector 486 mounted above and in alignment with the beam from an emitter-detector module 28 at one or more of the positions 430, 434, and 480. The reflector 486 reflects light emitted from the emitter-detector modules 28 back to the emitter-reflector modules. Use of reflector 486 permits a greater effective height for the beams of light from the emitter-detector modules 28 and also permits detection of the presence of a baseball or other object in the beams by virtue of the baseball or other object fully or partially blocking the light that is reflected from the reflector 486.

As with the previously described embodiments of the invention, an electronic signal from the detector (not shown) of one or more of the emitter-detector modules 28, which is indicative of the intensity, angle of incidence and other characteristics of the reflected light, may be provided to a microprocessor or computer (not shown). The microprocessor or computer, in turn, may determine the position of the baseball, via triangulation, for example, and compare the determined position of the baseball to the position of the upright 418 stored in memory. From the foregoing comparison, the microprocessor or computer may determine whether or not the baseball was batted out of the baseball playing field and therefore into foul territory. All of the information provided to the microprocessor or computer and all of the determinations made by the microprocessor or computer may be stored in a memory device, which may be included in or separate from the microprocessor or computer, for concurrent or later retrieval and reference via, for example, a visual display device.

Each of the embodiments of the present invention illustrated in FIGS. 1-10 can use either light emitted from a laser or less coherent light emitted by other sources. If light from a laser is used in the invention, the laser may be a Class 1 or Class 2 laser. Class 3 or higher lasers generally may not be used in the invention because of government regulations restricting the use of such lasers, particularly in open stadiums from which laser light might be reflected at or in the direction of aircraft. In domed or otherwise closed stadiums, however, it may be possible to use light emitted from Class 3 or higher lasers.

In one example embodiment of a laser sensor or “time of flight” unit that may be used in the present invention, the laser unit may have the following characteristics:

Measuring range—about 0.2 meters up to about 50 meters with natural surfaces, more than 100 meters achievable, depending on target reflectance.

Measuring accuracy—±about 2 millimeters under defined measuring conditions; otherwise ±about 3 millimeters (in a temperature range of about +15° C. up to about +30° C.); ±about 5 millimeters (in a temperature range of about −10° C. up to about +50° C.) with measuring time of about 0.16 up to about 6 seconds programmable or auto in Mode DT (Distance Tracking) or about 0.1 seconds in Mode DW (Distance Tracking with cooperative target at 10 hertz) on white surface or about 20 milliseconds in Mode DX (Distance Tracking with cooperative target at 50 hertz) on white surface (only LDM42A).

Resolution—about 0.1 millimeters, user scalable.

Reproducibility—about 0.5 millimeters with measuring time of about 0.16 up to about 6 seconds or about 0.1 seconds (10 hertz) on white surface Laser Class LK2 under DIN EN 60825-1:2001-11(<1 milliwatts, visible red)

Laser divergence—0.6 millirads.

One skilled in the art will appreciate that the foregoing and other numerical values set forth herein are given by way of example only and that other values may be used and other resolutions may result.

FIG. 11 illustrates an emitter-detector module 528 that is constructed in accordance with an eighth example of the present invention. As can be seen in FIG. 11, the emitter-detector module 528 is outwardly generally similar in construction to the emitter-detector modules 28, 128, and 228 of FIGS. 3, 4, and 5, respectively. In particular, the emitter-detector module 528 includes a generally cylindrical housing 548 with an upper open end that is closed by a cover 542. A power supply and communication sub-module 550 is mounted at the end of the housing 548 opposite the cover 542.

Inside the housing 548, however, the emitter-detector module 528 includes a proximity sensor unit 560 that both acts as a source for emitting electromagnetic radiation and a detector for detecting such electromagnetic radiation. The proximity sensor unit 560 may, for example, emit an upwardly directed and substantially vertical beam 564 of radio frequency and/or infrared electromagnetic radiation that is substantially parallel to an upright 18 or 20. The proximity sensor unit 560 is substantially smaller in diameter and circumference than the housing 548. The proximity sensor unit 560 may thus be positioned on the inner circumference of the housing adjacent to the edge of an upright 18 or 20 that defines the limit of the space through which a football must pass to qualify as, for example, an acceptable field goal. Also positioned on the inner circumference of the housing 548 are a plurality of emitting devices 568 that may emit either or both visible or non-visible (e.g., infrared) light. The proximity sensor unit 560 and the emitting devices 568 together form a circular array around the inner circumference of the housing.

Each of the emitting devices 568 emits an upwardly directed and substantially vertical beam of visible or non-visible light 566 that are substantially parallel to an upright 18 or 20. Together, the plurality of the emitting devices 568 emit a plurality of substantially parallel beams of visible or non-visible light 566 to illuminate the space directly above the emitter-detector module 528. Centered within the array of emitting devices 568 is a first detector unit 576, which may be a high speed color camera with a recording speed of two hundred or more frames per second. The first detector unit 576 detects and records light reflected from an object that interrupts one or more of the beams of light 566. The cover 542 of the emitter-detector module 528 is transparent to the light emitted by emitter devices 568 and to the radiation emitted by the proximity sensor unit 560. The emitter-detector module 528 may also include a shutter (not shown) mounted above the cover 542 to block at least certain types of electromagnetic radiation from the first detector unit 576 and/or the proximity sensor unit 560 when they are not in use.

In addition to the first detector unit 576, the emitter-detector module 528 may include a second detector unit 578. The second detector unit 578 may be attached to the outside of the housing 548, enclosed in a separate housing that is attached to the housing 548, or enclosed in a lateral extension of the housing 548. The second detector unit 578 may be an infrared camera with a recording speed of sixty or more frames per second. If the emitter devices 568 emit both visible and non-visible light, the second detector unit 578 may be used to detect infrared light reflected from an object that interrupts one or more of the beams of light 566. The second detector unit 578 may thus make determinations to supplement the determinations made by the first detector unit 576 and/or the proximity sensor unit 560 or to provide redundancy in the event one or both of the first detector unit 576 and/or the proximity sensor unit 560 experiences a malfunction.

The first detector unit 576 and the second detector unit 578 receive light reflected from the beams of light emitted by the emitter devices 568 and transmit electronic signals indicative of the intensity, angle of incidence and other characteristics of the reflected light to a microprocessor or computer 556 via one or more communication cables 558 or, alternatively, via wireless communication. The microprocessor or computer 556 uses the information in the signals from one or both of the first detector unit 576 and the second detector unit 578 to make a determination whether the reflected light received by the first detector unit 576 and/or the second detector unit 578 is reflected from a football or some other object, such as a bird. The microprocessor or computer 556 may also use the information in the signal from the first detector unit 576 and/or the second detector unit 578 and/or the proximity sensor unit 560 to determine, via triangulation, the position of the object, such as a football, from which the light received by the first detector unit 576 and/or the second detector unit 578 was reflected.

If the microprocessor or computer 556 determines that the reflected light received by the first detector unit 576 and/or the second detector unit 578 was reflected by a football, the microprocessor or computer may determine that some portion of the football entered one or more of the beam of light 566. From such a determination, the microprocessor or computer 556 may, in turn, determine that the football did not stay between the uprights 18 and 20 and therefore the attempted field goal was not successful. Alternatively or additionally, the microprocessor or computer 556 may determine the position of the football, via triangulation, for example, and compare the determined position of the football to the position of the uprights 18 and 20 stored in memory. From the foregoing comparison, the microprocessor or computer 556 may determine whether or not the attempted field goal was successful. All of the information provided to the microprocessor or computer 556 and all of the determinations made by the microprocessor or computer may be stored in a memory device, which may be included in or separate from the microprocessor or computer, for concurrent or later retrieval and reference via, for example, a visual display device.

Although the emitter-detector modules 28, 128, 228, and 528 may include sources for generating light, one or more emitter-detector modules 28, 128, 228, and/or 528 may share light generated by a common source and simply emit the light from the common source, rather than generating light in the modules. For example, in the embodiment of the invention shown in FIG. 1, a common source of light may be mounted at a location such as the intersection of the gooseneck 24 and the cross bar 22 or at the lower end of the gooseneck. Light from the common source could then be transmitted to one or more of the emitter-detector modules 28 via mirrors, fiber optic cables, and/or other light waveguides. In addition, in situations in which embodiments of the present invention use non-visible light, other forms of electromagnetic radiation, such as ultrasonic radiation, could be used in place of the non-visible light with appropriate radiation emitters and detectors.

Further, the various positions 30, 32, 34, 36, 180, 182, 390, 430, 434, and 480 of the emitter-detector modules 28, 128 and 228 illustrated in FIGS. 1-2 and 6-10 may be used in different combinations than those illustrated and/or described above according the requirements or preferences of different games, sports fields and/or game officials. Although the present invention is described and illustrated above as being used in the games of baseball and American football, the present invention may be used in any game in which the features of the invention may be of benefit.

Yet further, in an example embodiment of the invention, the aluminum tubing for the uprights 18 and 20 used a goal post 16 for the game of American football may be approximately four inches in diameter and the aluminum tubing for the cross bar 22 may be approximately six to eight inches in diameter. The emitter-detector modules 28, 128, 228, and 528 may then have the same or slightly smaller outer diameters as the uprights 18 and 20 of the goal post 16 and may also have overall heights short enough to allow the emitter-detector modules to be installed in the cross bar 22 in a vertical orientation. One skilled in the art will appreciate that the foregoing and other numerical values set forth herein are given by way of example only and that other values may be used and other resolutions may result. Also, the aluminum tubing or other tubular material used for any embodiment of the present invention may have a circular cross-section or any other cross-section incorporating a closed curve or may have a polygonal cross-section.

From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes, and/or modifications within the skill of the art are intended to be covered by the appended claims. 

1. A marker for a sports field comprising: an elongated substantially vertical device for marking a field position associated with a game playable on the sports field using an object that may become airborne, said field position being used to determine compliance of the object when airborne with a rule of the game; and a source for emitting an elongated generally vertical beam of electromagnetic radiation adjacent to the device to help mark said field position.
 2. A marker according to claim 1 further comprising an electromagnetic radiation detector for detecting electromagnetic radiation generated by said source and reflected by said object when passing through said beam of electromagnetic radiation.
 3. A marker according to claim 2 further comprising a position detector for determining an object position of said object based on the electromagnetic radiation reflected by said object when passing through said beam of electromagnetic radiation.
 4. A marker according to claim 3 further comprising a comparator for comparing said determined object position to stored data indicative of the field position to determine compliance of the object when airborne with a rule of the game.
 5. A marker according to claim 3 further comprising a recorder for recording the object position determined by the position detector.
 6. A marker according to claim 1 wherein said source is a first source and wherein said marker further comprises a second source for emitting a beam of electromagnetic radiation, the first source emitting electromagnetic radiation as visible light and the second source emitting electromagnetic radiation other than visible light.
 7. A marker according to claim 1 wherein said source generates only a single beam of electromagnetic radiation, said beam of electromagnetic radiation being a beam of visible light oriented substantially parallel to the device.
 8. A marker according to claim 1 wherein said elongated substantially vertical device includes a pole with a substantially vertical central axis and an exterior surface that is elongated in a direction along said central axis and that is at least partially defined by a closed curve in a plane substantially perpendicular to said central axis, said source being disposed within a space defined by the closed curve extended in opposed directions along said central axis.
 9. A marker according to claim 2 wherein said elongated substantially vertical device includes a pole with a substantially vertical central axis and an exterior surface that is elongated in a direction along said central axis and that is at least partially defined by a closed curve in a plane substantially perpendicular to said central axis, said source being disposed within a space defined by the closed curve extended in opposed directions along said central axis.
 10. A marker according to claim 1 wherein said elongated substantially vertical device includes a substantially vertical pole, said beam of electromagnetic radiation being generated as an extension of said pole.
 11. A marker according to claim 1 wherein said elongated substantially vertical device includes a substantially vertical pole mounted in a position that is vertically spaced above a surface of the sports field, said source being disposed below said pole and adjacent the surface of the sports field.
 12. A marker according to claim 1 wherein said elongated substantially vertical device includes a substantially vertical pole, said source being disposed adjacent an upper end of said pole.
 13. A marker according to claim 1 wherein said elongated substantially vertical device includes a substantially vertical pole mounted in a position that is vertically spaced above a surface of the sports field, said source being disposed adjacent a lower end of said pole.
 14. A marker according to claim 1 wherein said elongated generally vertical beam of electromagnetic radiation is substantially vertical, upwardly directed, and substantially parallel to said substantially vertical device.
 15. A marker for a sports field comprising: a device with an elongated substantially vertical portion for marking a field position associated with a game playable on the sports field using an object that may become airborne, said field position being used to determine compliance of the object when airborne with a rule of the game, said device including a member with an exterior surface that is elongated in one direction and that is defined by a closed curve in a plane substantially perpendicular to said one direction; a source for emitting a generally vertical beam of electromagnetic radiation adjacent to the device; and an electromagnetic radiation detector for detecting electromagnetic radiation generated by said source and reflected by said object when passing through said beam of electromagnetic radiation, said source and said electromagnetic radiation detector being disposed within the exterior surface of said member.
 16. A marker according to claim 15 wherein said source and said electromagnetic radiation detector are disposed adjacent to each other.
 17. A marker according to claim 15 further comprising a position detector for determining an object position of said object based on the electromagnetic radiation reflected by said object when passing through said beam of electromagnetic radiation.
 18. A method for marking a field position on a sports field associated with a game playable on the sports field using an object that may become airborne, said field position being used to determine compliance of the object when airborne with a rule of the game, said method comprising the steps of: positioning an elongated substantially vertical device to mark said field position; and emitting an elongated generally vertical beam of electromagnetic radiation adjacent to the device to help mark said field position.
 19. A method according to claim 18 further comprising the step of detecting electromagnetic radiation generated by said source and reflected by said object when passing through said beam of electromagnetic radiation.
 20. A method according to claim 19 further comprising the step of determining an object position of said object based on the electromagnetic radiation reflected by said object when passing through said beam of electromagnetic radiation.
 21. A method according to claim 20 further comprising the step of comparing said determined object position to stored data indicative of the field position to determine compliance of the object when airborne with a rule of the game. 